Means and method for varying the voltage of alternating currents.



E. H. SCHWARZ. MEANS AND METHOD FOR VARYING THE VOLTAGE 0F ALTERNATINGCURBENTS.

APPLICATION FILED APR. 5. I911.

Patented Dec. 7, 1915.

3 SHEETS-SHEET 1 Witnesses: Inventor 4 0 Elmer- H.5chwarz,

I M @W His Attorng E. H. SCHWARZ.

MEANS AND METHOD FOR VAHYING THE VOLTAGE 0F A'LTERNATING CURRENTAPPLICATION FILED APR. s. 1911.

1,163,268. Patented Dec. 7, 1915.

3 SHEETS-SHEET 2- Fig.6. r

Inventor: Elmer H.5chwarz,

His fitter-neg,

E. H. SCHWARZ. MEANS AND METHOD FOR VARYING THE VOLTAGE 0F ALTERNATINGCURRENTS.

APPLICATION FILED APR. s. 19H.

Patented Dec. 7, 1915.

3 SHEETSSHEET 3 Fi .H.

Witnesses:

zw w r m mm 0 n & e A VH xb .mr H 6 UNITED STATES PATENT OFFICE.

ELMER H. SCHWARZ, OF NEXV YORK, N. Y., ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

MEANS AND METHOD FOR VARYING THE VOLTAGE OF ALTERNATING- CURRENTS.

Specification of Letters Patent.

Patented Dec. '7, 1915.

Application filed April 6, 1911. Serial No. 619,211.

7tuZ-l whom it mag/concern iieit known that I, Emma H. Scrrwanz, acitizen of the United States, residing at New York, county of New York,State of New York, have invented certain new and useful Improvements inMeans and Methods for Varying the Voltage of Alternating Currents, ofwhich the following is a specification.

My invention relates to a means and method for varying the voltage ofalternating currents for various purposes.

It is often desirable, as for starting alternating current motors androtary converters, to use, for a short time only perhaps, a lowervoltage than is desirable in normal running conditions. Numerous schemeshave been proposed which involve the changing of connections, but mostof these schemes have objectional features. The scheme which I haveshown and later specifically described in this specification gives thesame phase to the starting currents as to the running currents, and atthe same time preserves the balance in the three-phase circuit by theuse of all the transformers in the starting as well as the runningposition.

' But my invention is not limited to obtaining low voltages for but ashort period of time as will be apparent from the description following.

Figures 1, :3 and 3 are vector diagrams, each representing in thecustomary manner the secondary coils of three transformers connected indelta in various ways; Fig. 4 diagrammatically shows the switchingarrangement; Figs. 5, 6 and 7 are diagrams representing variousconnections of the secondaries and their relation to the resistanceslater described; Fig. 8 shows diagrammatically the connections whereby ause may be made of the current which at times flows through theresistances; Figs. 9 and 10 show diagrammatically modifications of theconnections in Fig. 8; Fig. 11 illustrates transforme and controllerconnections embodying my invention, and Fig. 12 is a diagramrepresenting the connections of a plurality of sets of secondaries toobtain at the same time currents similar in phase but of differentelectromotive forces.

In Figs. 1, 2 and 8, the sides ab, ml and of represent by their lengthand direction, re spectively, the values and phase positions of theelectromotive forces impressed upon the respective secondary coils ofthe transformers, which are connected in delta. For simplicity we willassume that the sides of these triangles represent the actual secondarycoils of the transformers and their interconnections. The primary coilsof the transformers are not shown and may be connected as desired. Thearrows which are shown drawn parallel to the sides of the trianglespoint in the directions of corresponding ends of the coils,respectively, or we might say point in the directions in which theelectromotive forces across the secondaries are measured at all times,respectively.

If a triangle be inscribed in the triangle ABC of Fig. 1 so as toconnect the middle or half voltage points 1, 2, 3 of the triangle ABC,the electromotive force across any side of the inner triangle whenmeasured in given direction will be exactly in phase respectively withthe electromotive force of the side of the larger triangle with which itis parallel, when measured in a similar direction. This is shown by thedirection of the arrows for the inner triangle, and the value of theelectromotive forces across the sides of the inner triangle will berespectively proportional to the lengths of the sides of this triangle.i

If, now, the leads are firstv connected to the half voltage taps 2, 3,1and then connected to the full voltage points C, A and B, respectively,it will be seen that the electromotive forces impressed on the leads athalf voltage are 60 electrical degrees in advance in phase over those atfull voltage. In order to obviate this change in phase, I have in Fig. 2rearranged and connected the secondaries ab, 0d and ef in a new trianglein such a way that a triangle 1, 2, 3 can be inscribed, the sides ofwhich are respectively parallel to the sides of the larger triangle ABCof Fig. 1, when the triangles are traversed in the same direction,starting with point A of the larger triangle of Fig. l and with point 1of the inscribed triangle of Fig. 2. In other words, the side 12 of thesmaller triangle of Fig. 2 is parallel and in the same direction as theside cf of the larger triangle of Fig. 1, the side 23 of Fig. 2 isparallel and in the same direction as the side ab of Fig. 1 and the side31 of Fig. 2 is arallel and in the same direction as the si e 0d ofFig. 1. Therefore if a motor is connected for starting to the middlepoints 1, 2, 3 of the secondaries of the three transformers, when thesesecondaries are connected in accordance with Fig. 2, and then the samemotor leads are connected respectively to the points ABC, when thesecondaries are connected as shown in Fig. l, the electromotive forcesimpressed upon the motor windings in the two cases will be exactly inphase with each other respectively. It'will be seen in Fig. 2 thatalthough the secondaries have been connected differently from Fig. 1,nevertheless their positions in Fig. 2 are parallel respectively tothose of Fig. 1 and the arrows likewise point in the same direction. ThearroWs of the inscribed triangle of Fig. 2 indicate, as in the case ofFig. 1, that the electromotive force of each side" of the inner triangleis'measured in the same direction as the side of the outer triangle withwhich it is parallel.

In Fig. 3, the triangle of Fig. 2 is merely turned around so as to be inthe same position as the triangle of Fig. 1. It will be more readilyseen by Fig. 3 that the change from Fig. 1 to Fig. 2 consisted inreversing each side of triangle ABC of'Fig. 1 and then reconnecting thesides together in delta.

The ideas above set-forth may be utilized in various ways to obtaincurrents of the same phase but of diii'erent electromotive force. Thus asingle bank of transformers with a. single group of secondaries,provided with a suitable switching arrangement to make the properconnections, may-be used;

with such an arrangement either the higher electromotive force or thelower can be used at a time, but not both at the same time. Both,however, may be obtained by the use of a plurality of sets ofsecondaries reversely connected, or by the use of a plurality of sets oftransformers with their secondaries reversely connected. I haveimmediately following described a means for changing the connectionswhen but one set of secondaries is used.

Fig. 4 shows the switching arrangement for use with a single group ofsecondaries for connecting the motor or other leads k, Z, m to thepoints 1, 2, 3 of Fig. 2 for starting, and then connecting the sameleads respectively to the points ABC of Fig. 1 for running and at thesame time connecting the secondaries together in the proper way for eachposition, respectively. The switching device shown in Fig. 4 consists oftwo threepole double-throw switches or it may consist of one six-poledouble-throw switch.

The points of they switch are lettered in a manner corresponding to thedifierent points marked on Figs. 1 and 2. If two three-pole switches areused it is not necessary that they be thrown in exactly at the same timein either-direction. It is obvious that when the change is made fromFig. 2 to Fig. 1, it necessitates openingthe delta. This is likely to beundesirable where the primaries are connected in Y and where the voltageis comparatively high, as, in the case of an open delta under suchconditions, a magnetic disturbance will occur in the transformers whichis due to what is generally known as the third harmonic which results ina high voltage wave induced in the primary coils of the transformer whenthese primaries are connected to the circuit in Y at the end of a longdistance transmission line, if the secondaries should be open. I have,therefore, worked out a scheme to prevent the opening of the delta whenthe above-described changes, in the secondary connections are made. Thisis shown in Figs. 5 and 6 of the attached drawing. In Fig. 5 thesecondary coils are connected in the manner of Fig. 1. In addition tothe ordinary direct connection between the ends of the secondaries atthe points of the triangle, an additional connection is made from theend of one coil to the beginning of the" next by a resistance 1'. \Vhenthe connections between the secondaries are broken at the points ABC,the delta is not opened, as the circuit is kept closed by theresistances made is shown in Fig. 7, where wesee we have simply placedone of the resistances 7' across each of the secondaries. Instead ofresistances 1' We might use reactive coils, but in either case theresistances or reactances should be low enough to-prevent thirdharmonies from attaining any considerable value. The resistances orreactive coils are permanently connected with the endsof the sides ofthe secondaries as shown in Fig.- 5, and when the switching mechanism ofFig. I 4 is used there will be produced at starting theconnections shownin Fig. 7 and at running the connections shown in Fig. In

coils will be simply short circuited. The arrangement shown in Fig. 7suggests a novel substitute for the resistances or reactive coilsconnected across the sides of the tri-' angle. This novel use is shownin Fig. 8

where the shunt circuits are led through the cally throw the switch tothe running position' after which the small motor would. stop as itscoils would be short circuited as in the manner of the resistances shownin Fig. 5.

r. This is shown in Fig. 6. Now what happens when the connections ofFig. 2 are the latter case the resistances or reactive Fig. 9 is amodification of Fig. 8 as to the means for securing current for thesmall switch motor. Instead of the shunt circuits around the sides ofthe triangle leading directly to the windings of the switch motor theyare connected, as in Fig. 9, across compensators or auto-starters andfrom these the motor receives its energy, at either a reduced orincreased voltage, a method well known to those experienced inelectricity. This would allow of a certain independence between thereactance of the compensator winding and the voltage of the switchmotor. Resistances could be substituted for the compensator coils ofFig. 9, and fractional voltages for the starting motor winding could betaken off of these resistances with somewhat the same advantages as withthe compensator coils.

Fig. 10 is still another modification of Fig. 8. Here instead ofauto-transformers, as in Fig. 9, regular transformers are used, theprimaries of which are placed in shunt circuit around the sides of thetriangle. The secondaries are then connected in delta and the leads w y2' are led to the motor by the regular three-phase three-wire method.Instead of three single transformers, as shown in Fig. 10, a singlethree-phase transformer might be used. The advantage of the method ofFig.-l0 lies in the fact that only three wires need to be used betweenthe transformers and the small switch motor and that the windings of theswitch motor can be permanently connected in either Y or delta.

In Fig. 11 of the attached drawings, I have shown the development of acontroller and a diagram of connections corresponding to those moregenerally shown in Figs. 5 and 8. The stationary fingers are indicatedby letters and numbers d, e, b, a, f, 0 1 is, 2 Z, 3 and m, from top tobottom in the order named. The letters and numbers correspond to thesame letters and numbers on the different Figs. 1 to 10, inclusive. Thefingers cooperate with the movable contact segments T to the left whichare mounted on' the controller drum. Transformer windings are shown tothe right of the drawing of Fig. 11, and are lettered similarly to thoseof Figs. 1 to 10, inclusive. A switch or controller motor M is shownabove the movable contact segments T with windings for the three phasesand squirrel-cage armature rotatable inside of them. The connectionsbetween the transformer secondaries and the switch motor M correspond tothose of Fig.

8. These are not preferable connections but they are shown forsimplicitys sake. Those of Figs. 9 and 10 are more desirable. It will beseen from Fig. 11 that the switch motor is out out of circuit, or itswindings short circuited in the running position of the rotary or motor.It will be noted that the transformer secondaries are connected togethersimilarly in the running and off positions. Of course, the movablesegments for the off position might be arranged so that the secondariesare changed in connection from the running to the off position andconnected the same as for the starting position. lVith the latterarrangement the switch motor, if connected as in Figs. 9 and 10, mightbe started in the off position so that it would not be necessary to turnthe controller by hand from the off to the starting positions and thecontroller could be operated entirely by the motor from the ofl? to therunning positions. This would require a widening of the movable segmentscorresponding to the starting position, and a switch in the switch motorcircuit.

As before suggested, my invention covers also a plurality of secondariesfor supplying at the same time in phase currents of higher and lowerelectromotive forces.

Fig. 12 represents diagrammatically the connections of two sets ofsecondaries to ob tain such currents. As in the preceding figures noprimary is shown. These secondaries may have a common primary, or eachsecondary may have its own primary, in which latter case the primarieswill be similarly connected to the line. I have shown here two sets ofsecondaries ab, 0d, ef and a'b', c'al and 6' the secondaries of thefirst set are connected in delta similar to the connections of thesecondaries as previously described for normal running condition, andthe secondaries of the second set are connected as the secondariespreviously described for supplying the lower electromotive forces. Itwill also be observed that from each of the sets of secondaries the tapsare taken from the same points as previously described, that is the tapsfrom the first set are taken from the corners, and the taps from thesecond set are taken from the mid points. Thus it will be seen there aresupplied at all times currents in phase and of the two electromotiveforces. These currents may be utilized as will be apparent in variousways as desired.

Although I have shown and described the low voltage as one-half the fullvoltage, it will be understood, of course, that this relation of thevalues is not absolutely neces sary; that it may be desirable at timesto use this method of connecting to produce other voltage relations.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is,

to interconnected windings, then at approximately the same time bothdisconnecting the leads from the windings and reversing the windings,and connecting the leads to other points of the windings.

3. The method of varying the voltage of a polyphase system, whichconsists in first connecting the leads to approximately half voltagepoints of delta-connected windings, then reversing the windings, andconnecting the leads to the ends of said windings.

i. The method of deriving two polyphase currents of the same phase butdiiferent electromotive forces from a single set of three phase deltaconnected transformer windings,

which consists in taking the lower voltage 4 connections from mid.points of the windings, and taking the higher voltage connections fromthe ends of said windings, their connections being reversed relative totheir first mentioned connection.

5. The combination of a plurality of windings connected in delta,interior taps from said windings, a plurality of conductors, and meansfor connecting the conductors to the interior taps, and for reversingthe windings and connecting the conductors to the ends of said windings.

6. The combination of a plurality of windings connected in delta, tapsfrom mid points of said windings, a plurality of conductors, and meansfor connecting the conductors to the taps from mid points, and forreversing the windings and connecting the conductors to the ends of saidwindings.

7 The method of deriving two polyphase currents of the same phase butdifferent electromotive forces from a plurality of three phase windingsconnectedin delta, which consists in taking the lower voltageconnections from mid points of the windings and the higher voltageconnections from the ends of the windings, the windings in the two casesbeing reversed with respect to each other.

8. The combination with a plurality of conductors, of a pluralitv ofsingle phase sources of supply capable of supplying three phase energy,and means for connectingsaid conductors to mid voltage points of aplurality of said sources of supply connected in a delta relation and tohigher voltage points of a plurality of said sources connected in adelta relation, the respectivemembers of the two deltas being relativelyreversed.

9. The combination of a plurality of windings connected in delta,interior taps from said windings, a plurality of conductors, means forconnecting the conductors to the interior-taps, and for reversing thewindings and connecting the conductors to the ends of said windings, andmeans for preventing the complete disconnection of the windings fromthemselves.

10. The combination of a plurality of windings connected in delta,interior taps from said windings, a plurality of conductors, means forconnecting the conductors to the interior taps, and for reversing thewindings and connecting the conductors to the ends of said windings, andimpedances connecting the ends of the windings.

11. The combination of a plurality of windings connected in delta,interior taps from said windings, a plurality of conductors, means forconnecting the conductors to the interior taps, and for reversing thewindings and connecting the conductors to the ends of said windings, amotor, and connections to the ends of the windings for supplying themotor.

12. The combination of a plurality of windings connected in delta,interior taps from said windings, a plurality of conductors, means forconnectingthe conductors to the interior taps, and for reversing thewindings and connecting the conductors to the ends of said windings, aninduction motor, and connections for supplying the motor, each set ofconnections being to two windings.

In witness whereof, I have hereunto set my hand this third day of April,1911.

ELMER H. SCHWARZ.

Witnesses:

HALL l HOXIE, T. A. DEMPSEY.

Copies of this patent may he obtained for five cents each, by addressingthe "Commissioner of Patents. Washington, D. C.

